A wide variety of articles that incorporate the phenomenon of retroreflectivity have been developed for a wide array of uses. Retroreflective articles have the ability to return a substantial portion of incident light back towards the light source. This unique ability has promoted widespread use of retroreflective safety articles. Besides traffic and warning signs and the like, a wide variety of clothing and similar articles such as backpacks, and the like have incorporated retroreflective articles into them. Persons who work or exercise near motor vehicle traffic need to be conspicuously visible so that they do not get struck by passing motor vehicles. When retroreflective articles are worn, the retroreflectivity highlights a person's presence by retroreflecting light from motor vehicle headlamps.
Retroreflective articles typically have an optical lens element layer, a polymeric binder layer, a reflective layer, and may also have a substrate layer. The optical lens elements commonly are microspheres that are partially embedded in the polymeric binder layer. The reflective layer typically is aluminum, silver, or a dielectric mirror that usually is disposed on the embedded portions of the microspheres. Light striking the front surface of the retroreflective article passes through the microspheres and is reflected by the reflective layer to re-enter the microspheres where the light's direction is then altered to travel back towards the light source. Thus, for example, when a vehicle's headlamps strike a retroreflective article, some of the light from the headlamps is reflected back to the driver of the vehicle.
It is generally not necessary, or even desirable, that an entire worn article be retroreflective, so retroreflective appliqués are often used. These retroreflective appliqués can then be attached to an article of clothing or other article to prepare a retroreflective article. In some instances, retroreflective appliqués have been made by partially embedding a microsphere layer in a thermoplastic carrier web, applying a reflective material over the microspheres' protruding portions, and then forming a binder layer over the coated microspheres. Often a pressure sensitive adhesive is applied on the binder layer's back surface, and a release liner is placed over the adhesive until the appliqué is secured to a substrate. The completed appliqué (also sometimes referred to as a transfer sheet) is supplied to a garment assembler in this form, and the garment assembler secures the appliqué to an article of clothing by removing the release liner and adhering the appliqué to an outer surface of the article of clothing. The carrier is then separated from the appliqué to expose the microspheres so that the appliqué can retroreflect light.
In order to decrease the susceptibility of retroreflective articles to corrosion and/or staining and improve durability and launderability, a number of techniques have been used to protect the reflective material layer. Examples of such techniques include encapsulation of the reflective article with a cover film as in U.S. Pat. No. 4,678,695 (Tung et al.). Other techniques have taught the use of layers or coatings to specifically protect the reflective layer such as U.S. Pat. No. 5,824,390 (Ochi et al.) which teaches the use of a thin film containing a coupling agent which is formed on the vapor-deposited metal layer prior to superposing the thermoformable support sheet to the bead layer, U.S. Pat. No. 5,474,827 (Crandall et al.) which incorporated a compound comprising an aromatic bidentate moiety in the binder layer which is chemically associated with the retroreflective elements, U.S. Pat. No. 5,812,317 (Billingsley et al.) which incorporated a polymeric intermediate layer between the microspheres of the retroreflective article, and U.S. Pat. No. 7,723,452 (Hooftman et al.) which teaches a method of treatment of retroreflective sheets with treatment compositions that comprise fluorinated compounds having one or more silyl groups, and an auxiliary compound. Another technique is described in U.S. Pat. No. 6,172,810 (Fleming et al.) which describes retroreflective articles with a layer of optical elements and multilayer reflective coating disposed on the optical elements, the multilayer reflective coating having multiple polymer layers with different refractive indices.
In U.S. Pat. No. 6,355,302, a different continuous process is described for making retroreflective articles in which a fabric is coated with a binder material and aluminized beads are applied to the coating of binder material. An etching station removes exposed portions of the aluminized coating from the beads after the binder material is allowed to solidify.